Buried channel semiconductor device and method for manufacturing the same

ABSTRACT

A method for manufacturing a semiconductor device includes forming one or more fins extending in a first direction over a substrate. The one or more fins include a first region along the first direction and second regions on both sides of the first region along the first direction. A dopant is implanted in the first region of the fins but not in the second regions. A gate structure overlies the first region of the fins and source/drains are formed on the second regions of the fins.

This application discloses subject matter similar to that disclosed inMWE Docket No. 095714-0035 filed concurrently with this application. MWEDocket No. 095714-0035 is incorporated by reference in this applicationin its entirety.

As the semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, higher performance,and lower costs, challenges from both fabrication and design issues haveresulted in the development of three-dimensional designs, such as a finfield effect transistor (FinFET). FinFET devices typically includesemiconductor fins with high aspect ratios and in which channel andsource/drain regions of semiconductor transistor devices are formed. Agate is formed over and along the sides of the fin structure (e.g.,wrapping) utilizing the advantage of the increased surface area of thechannel and source/drain regions to produce faster, more reliable andbetter-controlled semiconductor transistor devices. In some devices,strained materials in source/drain (S/D) portions of the FinFETutilizing, for example, silicon germanium (SiGe), silicon phosphide(SiP) or silicon carbide (SiC), may be used to enhance carrier mobility.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 is an exemplary process flow chart for manufacturing asemiconductor FET device having a fin structure (FinFET) according to anembodiment of the present disclosure.

FIGS. 2-16 show an exemplary method for manufacturing a semiconductordevice and a semiconductor device in accordance with an embodiment ofthe disclosure.

FIG. 17 shows a mixer circuit according to an embodiment of thedisclosure.

FIG. 18 shows an apparatus including a mixer circuit according to anembodiment of the disclosure.

FIGS. 19A-19D are graphs illustrating the gate voltage versus the draincurrent of a device including a FinFET according to the disclosure.

FIG. 20 is a graph illustrating the linearity of a device including aFinFET according to the disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific embodiments or examples of components andarrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. For example, dimensions of elements are not limited to thedisclosed range or values, but may depend upon process conditions and/ordesired properties of the device. Moreover, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed interposing the first and second features, suchthat the first and second features may not be in direct contact. Variousfeatures may be arbitrarily drawn in different scales for simplicity andclarity.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The device may be otherwise oriented (rotated 90 degrees orat other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. In addition, the term“made of” may mean either “comprising” or “consisting of.”

FinFET devices have a larger flicker noise than bulk CMOS devices.Analog/RF circuits require lower noise and higher linearity MOS devices.The present disclosure is directed to a transistor providing lower noiseand higher linearity MOS devices.

Examples of devices that can benefit from one or more embodiments of thepresent disclosure are semiconductor devices. Such a device, forexample, is a FinFET device. The FinFET device, for example, may be acomplementary metal-oxide-semiconductor (CMOS) device comprising aP-type metal-oxide-semiconductor (PMOS) FinFET device and an N-typemetal-oxide-semiconductor (NMOS) FinFET device. In particular, aGilbert-cell mixer can benefit from the present disclosure. Thefollowing disclosure will include a FinFET example to illustrate variousembodiments of the present application. It is understood, however, thatthe application should not be limited to a particular type of device,except as specifically claimed.

An exemplary method for manufacturing a semiconductor FET device havinga fin structure (FinFET) according to an embodiment of the presentdisclosure is illustrated in FIG. 1. An exemplary method 100 includes anoperation 102 of forming a one or more fins over a substrate and anoperation 104 of implanting a dopant into the one or more fins. Anoperation 106 of forming a gate structure over the one or more fins isperformed after the implanting operation. Source/drains are formed onthe one or more fins on either side of the gate structure in anoperation 108.

To fabricate one or more fins according to one embodiment, a mask layer14 is formed over a substrate 12, as illustrated in FIG. 2. The masklayer 14 is formed by, for example, a thermal oxidation process and/or achemical vapor deposition (CVD) process. The substrate 12 is, forexample, a p-type silicon substrate with an impurity concentration in arange of about 1×10¹⁵ cm⁻³ to about 2×10¹⁵ atoms cm⁻³. In otherembodiments, the substrate 12 is an n-type silicon substrate with animpurity concentration in a range of about 1×10¹⁵ cm⁻³ to about 2×10¹⁵atoms cm⁻³. The mask layer 14 includes, for example, a pad oxide (e.g.,silicon oxide) layer 16 and a silicon nitride mask layer 18 in someembodiments.

Alternatively, the substrate 12 may comprise another elementarysemiconductor, such as germanium; a compound semiconductor includingIV-IV compound semiconductors such as SiC and SiGe, III-V compoundsemiconductors such as GaAs, GaP, GaN, InP, InAs, InSb, GaAsP, AlGaN,AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; or combinations thereof.In one embodiment, the substrate 12 is a silicon layer of an SOI(silicon-on insulator) substrate. When an SOI substrate is used, thefins may protrude from the silicon layer of the SOI substrate or mayprotrude from the insulator layer of the SOI substrate. In the lattercase, the silicon layer of the SOI substrate is used to form the fins.Amorphous substrates, such as amorphous Si or amorphous SiC, orinsulating material, such as silicon oxide may also be used as thesubstrate 12. The substrate 12 may include various regions that havebeen suitably doped with impurities (e.g., p-type or n-typeconductivity).

The pad oxide layer 16 may be formed by using thermal oxidation or a CVDprocess. The silicon nitride mask layer 18 may be formed by a CVD,plasma-enhanced chemical vapor deposition (PECVD), an atmosphericpressure chemical vapor deposition (APCVD), a low-pressure CVD (LPCVD),a high density plasma CVD (HDPCVD), an atomic layer deposition (ALD), aphysical vapor deposition (PVD), such as a sputtering method, and/orother processes.

The thickness of the pad oxide layer 16 is in a range of about 2 nm toabout 15 nm and the thickness of the silicon nitride mask layer 18 is ina range of about 2 nm to about 50 nm in some embodiments. A mask pattern20 is further formed over the mask layer 14. The mask pattern 20 is, forexample, a resist pattern formed by lithography operations.

By using the mask pattern 20 as an etching mask, a hard mask pattern ofthe pad oxide layer 16 and the silicon nitride mask layer 18 is formed.The width of the hard mask pattern is in a range of about 5 nm to about40 nm in some embodiments. In certain embodiments, the width of the hardmask patterns is in a range of about 7 nm to about 12 nm.

By using the hard mask pattern as an etching mask, the substrate 12 ispatterned into a plurality of fins 24, as shown in FIG. 3, by trenchetching using a dry etching method and/or a wet etching method to formtrenches 26. A height of the fins 24 is in a range of about 20 nm toabout 300 nm. In certain embodiments, the height is in a range of about30 nm to about 60 nm. When the heights of the fins 24 are not uniform,the height from the substrate may be measured from the plane thatcorresponds to the average heights of the fins 24. The width of each ofthe fins 24 is in a range of about 7 nm to about 15 nm.

In this embodiment, a bulk silicon wafer is used as the substrate 12.However, in some embodiments, other types of substrate may be used asthe substrate 12. For example, a silicon-on-insulator (SOI) wafer may beused as a starting material, and the insulator layer of the SOI waferconstitutes the substrate 12 and the silicon layer of the SOI wafer isused for the fins 24.

As shown in FIG. 3, eight fins 24 are disposed over the substrate 12.However, the number of fins is not limited to eight. There may be as fewas one fin and more than eight fins. In addition, one or more dummy finsmay be disposed adjacent to the sides of the fins to improve patternfidelity in the patterning processes. The width of each fin 24 is in arange of about 5 nm to about 40 nm in some embodiments, and may be in arange of about 7 nm to about 15 nm in certain embodiments. The width oftrenches 26 between adjacent fins is in a range of about 5 nm to about80 nm in some embodiments, and may be in a range of about 7 nm to about15 nm in other embodiments. One skilled in the art will realize,however, that the dimensions and values recited throughout thedescriptions are merely exemplary, and may be changed to suit differentscales of integrated circuits.

In certain embodiments, the FinFET device is a P-type FinFET, while inother embodiments, the device is an N-type FinFET, depending on thedopant types used in the source/drains and channel.

After forming the fins 24, an isolation insulating layer 22 is formed intrenches 26 between the fins 24 and overlying the fins 24, so that thefins 24 are buried in isolation insulating layer 22, as illustrated inFIG. 4. The isolation insulating layer 22 is also referred to as ashallow trench insulation (STI).

The isolation insulating layer 22 includes one or more layers ofinsulating materials such as silicon oxide, silicon oxynitride orsilicon nitride, formed by LPCVD (low pressure chemical vapordeposition), plasma-CVD or flowable CVD. In the flowable CVD, flowabledielectric materials instead of silicon oxide are deposited. Flowabledielectric materials, as their name suggest, can “flow” duringdeposition to fill gaps or spaces with a high aspect ratio. Usually,various chemistries are added to silicon-containing precursors to allowthe deposited film to flow. In some embodiments, nitrogen hydride bondsare added. Examples of flowable dielectric precursors, particularlyflowable silicon oxide precursors, include a silicate, a siloxane, amethyl silsesquioxane (MSQ), a hydrogen silsesquioxane (HSQ), anMSQ/HSQ, a perhydrosilazane (TCPS), a perhydro-polysilazane (PSZ), atetraethyl orthosilicate (TEOS), or a silyl-amine, such as trisilylamine(TSA). These flowable silicon oxide materials are formed in amultiple-operation process. After the flowable film is deposited, it iscured and then annealed to remove un-desired element(s) to form siliconoxide. When the un-desired element(s) is removed, the flowable filmdensifies and shrinks. In some embodiments, multiple anneal processesare conducted. The flowable film is cured and annealed more than once.The flowable film may be doped with boron and/or phosphorous. Theisolation insulating layer 22 may be formed by one or more layers ofSOG, SiO, SiON, SiOCN and/or fluoride-doped silicate glass (FSG) in someembodiments.

A planarization operation is performed so as to remove part of theisolation insulating layer 22. As illustrated in FIG. 5, theplanarization operation may include a chemical mechanical polishing(CMP) and/or an etch-back process.

The mask layer 14 may be removed, and an upper portion of the isolationinsulating layer 22 is further removed so that the channel region (upperportion) of the fins 24 is exposed, as shown in FIG. 6.

In certain embodiments, removal of the mask layer 14 and partiallyremoving the isolation insulating layer 22 may be performed using asuitable etching process. For example, the mask layer 14 may be removedby a wet etching process, such as, by dipping the substrate inhydrofluoric acid (HF) or phosphoric acid (H₃PO₄). On the other hand,the partially removing the isolation insulating layer 22 may beperformed using a dry etching process. For example, a dry etchingprocess using CHF₃ or BF₃ as etching gases may be used.

An isometric view of the device 10 showing the fins 24 exposed from theisolation insulating layer 22 is depicted in FIG. 7. To simplify thedisclosure, only three fins are shown in FIG. 7. The exposed portions ofthe fins 24 comprise two regions. A first region 36 in a central portionof the fin 24 is where a gate structure will be formed, and a secondregion 38 at the peripheral portions of the fin 24 is where source/drainregions will be formed.

FIG. 8 depicts a cross section taken along line A-A of FIG. 7. A resistlayer 44, such as a photoresist, is formed over the fins 24, as shown inFIG. 9A. The resist layer 44 is patterned by exposure to actinicradiation and subsequent development to form openings 54 exposing thetop of the fins 24. The openings 54 are formed over the first regions 36of the fins 24 and the second regions 38 of the fins 24 are covered bythe resist 44. A plan view of the resist layer 44 with openings 54 isshown in FIG. 9B.

Using the patterned resist layer 44, as a mask, a dopant 46 is implantedinto the fins 24 by ion implantation, as shown in FIG. 10. The fins 24are masked so that the dopant is implanted into the first region 36 ofthe fin, which will become the channel of the FinFET. In certainembodiments, the dopant is implanted at an energy ranging from about 1KeV to about 100 KeV.

In certain embodiments, the dopant 46 is an N-type dopant selected fromthe group consisting of P, As, and Sb. In particular, the N-type dopantmay be P in certain embodiments. In other embodiments, the dopant 46 isa P-type dopant selected from the group consisting of B, BF₂, Al, andGa. The concentration of the dopant 46 implanted in the first region 36is about 1.5×10¹⁶ to 2.0×10²⁰ atoms cm⁻³. In certain embodiments, theconcentration of the dopant 46 in the first region 36 is about 1.7×10¹⁷to 1.7×10¹⁹ atoms cm⁻³. The concentration of the dopant 46 in the firstregion 36 is about 1×10¹⁸ to 2×10¹⁸ atoms cm⁻³ in certain embodiments.As shown in FIG. 11, the implanted dopant 46 may form a doped region 48centered at region in the fin located at about 15 to 20 nm in the heightH direction from a top of the fin 24 and 3 to 7 nm in a fin thicknessdirection W from a sidewall of the fin 24. The doped region 48 forms aburied channel.

Adverting to FIG. 12, which is a view corresponding to a cross sectionalong line B-B in FIG. 7, illustrating a buried channel doped region 48.A gate electrode structure will subsequently be formed overlying theburied channel doped region 48, and source/drain regions will be formedoverlying second regions 38 on sides of the first region 36. The channellength L corresponds to the length of the first region 36. The channellength L may range from about 7 nm to about 16 nm in some embodiments.The channel length L also corresponds to the gate length of thesubsequently formed transistor.

A gate structure 28 is subsequently formed over the first region 36 ofthe fins, as shown in FIG. 13. The gate structure formation process mayinclude the operations of depositing a gate dielectric 32, depositing agate electrode 30, patterning the gate electrode, lightly doped drain(LDD) implantation, and annealing. Sidewall spacers 34 are subsequentlyformed on the gate structure 28, and source/drain implantation andannealing are performed. FIG. 14 corresponds to a cross section takenalong line a-a of FIG. 13, showing the arrangement of the fins 24 andthe gate electrode structure 28.

In certain embodiments, the FinFET can be fabricated using a gate firstmethod or a gate last method. In embodiments using a high-k dielectricand a metal gate (HK/MG), a gate last method is employed to form thegate electrode. In the gate last method, a dummy gate is formed, thedummy gate is subsequently removed at a later operation after a hightemperature annealing operation, and the high k dielectric and a metalgate (HK/MG) is formed.

According to embodiments of the disclosure, the high k gate dielectric32 may comprise HfO₂, HfSiO, HfSiON, HfTaO, HfSiO, HfZrO, zirconiumoxide, aluminum oxide, hafnium dioxide-alumina (HfO₂—Al₂O₃) alloy, othersuitable high-k dielectric materials, or combinations thereof. The metalgate material may comprise one or more layers of Ti, TiN,titanium-aluminum alloy, Al, AN, Ta, TaN, TaC, TaCN, TaSi, and the like.

The gate dielectric 32 may comprise one or more layers of silicon oxide,silicon nitride, silicon oxynitride, high-k dielectric material, othersuitable dielectric material, and/or combinations thereof. The gateelectrode 30 in certain embodiments is formed of polysilicon and mayinclude a hard mask formed over the gate electrode. The hard mask may bemade a suitable hard mask material, including SiO₂, SiN, or SiCN. Insome embodiments, a thickness of the gate dielectric layer is in a rangeof about 5 nm to about 20 nm, and in a range of about 5 nm to about 10nm in other embodiments. The gate electrode structure may compriseadditional layers such as interfacial layers, capping layers,diffusion/barrier layers, dielectric layers, conductive layers, andother suitable layers, and combinations thereof. In addition topolysilicon, in some embodiments, the gate electrode 30 includes one ormore layers of any other suitable material, such as aluminum, copper,titanium, tantalum, tungsten, molybdenum, tantalum nitride, nickelsilicide, cobalt silicide, TiN, WN, TiAl, TiAlN, TaCN, TaC, TaSiN, metalalloys, other suitable materials, or combinations thereof. In someembodiments, a thickness of the gate electrode layer is in a range ofabout 50 nm to about 400 nm, and may be in a range of about 100 nm to200 nm.

In some embodiments, the sidewall spacers 34 are used to offsetsubsequently formed doped regions, such as source/drain regions. Thesidewall spacers 34 may further be used for designing or modifying thesource/drain region (junction) profile. The sidewall spacers 34 may beformed by suitable deposition and etch techniques, and may comprisesilicon nitride, silicon carbide, silicon oxynitride, other suitablematerials, or combinations thereof.

A blanket layer of a side-wall insulating material may be formed by CVD,PVD, ALD, or other suitable technique. Then, an anisotropic etching isperformed on the side-wall insulating material to form a pair ofside-wall insulating layers (spacers) 34 on two main sides of the gatestructure. The thickness of the side-wall insulating layers 34 is in arange of about 5 nm to about 30 nm in some embodiments, and in a rangeof about 10 nm to about 20 nm in other embodiments. As shown in FIG. 13,the side wall insulating layer may not be formed over the regions of thefin that is to become the source and drain.

The second region 38 of the fins not covered with the gate structure 28are subsequently etched to remove the portion of the fins above the STIregion 22, as shown in FIG. 15. Suitable photolithographic and etchingtechniques can be used to remove the second region 38 of the fins.

In certain embodiments, raised source/drain regions 40 are subsequentlyformed overlying the etched portion of the fins 24, as shown in FIG. 16,providing a FinFET semiconductor device 10. The raised source/drainregions may be formed by one or more epitaxy or epitaxial (epi)processes, such that Si features, SiC features, SiGe features, SiPfeatures, SiCP features, or Group III-V semiconductor material on Si EPIor other suitable features are formed in a crystalline state on thefins. The epitaxy processes include CVD deposition techniques (e.g.,vapor-phase epitaxy (VPE) and/or ultra-high vacuum CVD (UHV-CVD)),molecular beam epitaxy, and/or other suitable processes.

In some embodiments of the disclosure, source/drain electrodes areformed contacting the respective source/drain regions. The electrodesmay be formed of a suitable conductive material, such as copper,tungsten, nickel, titanium, or the like. In some embodiments, a metalsilicide is formed at the conductive material and source/drain interfaceto improve conductivity at the interface. In one example, a damasceneand/or dual damascene process is used to form copper-based multilayerinterconnection structures. In another embodiment, tungsten is used toform tungsten plugs.

Subsequent processing according to embodiments of the disclosure mayalso form various contacts/vias/lines and multilayer interconnectsfeatures (e.g., metal layers and interlayer dielectrics) on thesemiconductor substrate, configured to connect the various features orstructures of the FinFET device. For example, a multilayerinterconnection includes vertical interconnects, such as conventionalvias or contacts, and horizontal interconnects, such as metal lines.

In certain embodiments, the epitaxial growth of the source/drain regionsis continued until the individual source/drain regions merge together toform a FinFET semiconductor device with merged source/drain regions.

In another embodiment of the present disclosure, a semiconductor device,such as a Gilbert-cell mixer 50, is provided, as illustrated in FIG. 17.The Gilbert-cell mixer includes a plurality of transistors M₁, M₂, M₃,M₄, M₅, M₆ electrically connected to each other. At least one of thetransistors includes a buried-channel FinFET according to the embodimentpreviously disclosed herein. The Gilbert-cell mixer 50 further includesinductors L₁, L₂ and capacitors C₁, C₂, as shown in FIG. 17.

In an embodiment of a Gilbert-cell mixer according to the presentdisclosure, as shown in FIG. 17A, the right-hand side of the circuitdiagram is a mirror image of the left-hand side. Inductors L1 and L2 areconnected to transistors M3 and M6, respectively. Capacitor C1 isconnected between inductor L1 and transistor M3, and is connected totransistor M5. Capacitor C2 is connected between inductor L2 andtransistor M6, and is connected to transistor M4. The current outputs oftransistors M3 and M4 are connected to transistor M1, the current outputof which is connected to ground. The current outputs of transistors M5and M6 are connected to transistor M2, the current output of which isconnected to ground. In certain embodiments, each of transistors M1, M2,M3, M4, M5, M6 can be a buried-channel FinFET transistor.

The Gilbert-cell mixer 50 may be incorporated into an apparatus 52including operational amplifiers, analog-to-digital converters (ADC),digital-to-analog converters (DAC), RF synthesizers, and processors, asshown in FIG. 18. The apparatus in FIG. 18 is an RF full circuit blockincluding a mixer, local area network (LAN), phase locked loop (PLL),voltage control oscillator (VCO), and ADC. In certain embodiments, alltransistors in the apparatus are buried-channel FinFET transistors.

FinFET devices with a buried-channel implant can provide up to a 10times reduction in flicker noise and reduced power consumption of up to40% over bulk CMOS devices. The use of buried-channel FinFET transistorsaccording to the present disclosure in a Gilbert-cell mixer can provideimproved mixer linearity with up to 10 times less flicker noise.Gilbert-cell mixers using the disclosed buried-channel FinFETtransistors provide a 2-3 times improvement in linearity coupled withincreased drain current and power efficiency at a reduced thresholdvoltage of less than half the threshold voltage of a bulk CMOS device.At the same current level, a mixer having buried-channel FinFETtransistors according the present disclosure may improve the linearityby up to 3 dB. At the same linearity, a mixer having buried-channelFinFET transistors may reduce the dc current of the mixer by about 40%.FIGS. 19A, 19B, 19C, and 19D show the gate threshold voltage versusdrain current of a mixer including 16 nm gate length FinFETs having aburied channel according the present disclosure in comparison to astandard device having 16 nm gate length FinFETs. A comparison of thelinearity of a mixer having 16 nm gate length FinFETs having a buriedchannel according to the present disclosure (BC) and a standard device(C) having 16 nm gate length FinFETs is illustrated in FIG. 20. In FIGS.19A-19D and 20, it is found that buried-channel device has a more linearincrease in current with increased voltage, whereas the conventionaldevice has an exponential increase in current with increased voltage.Thus, devices according to the present disclosure have increasedlinearity and low-noise, and non-sensitivity with trap fluctuation.

In one embodiment of the present disclosure, a method for manufacturinga semiconductor device is provided. The method includes forming one ormore fins extending in a first direction over a substrate. The one ormore fins include a first region along the first direction and secondregions on both sides of the first region along the first direction. Adopant is implanted in the first region of the fins but not in thesecond regions. A gate structure is formed overlying the first region ofthe fins, and source/drains are formed on the second regions of thefins.

In another embodiment of the disclosure, a semiconductor device isprovided including one or more fins extending in a first direction overa substrate. The one or more fins include a first region along the firstdirection and second regions on either side of the first region alongthe first direction, and the first region of the fins includes a dopantin a concentration of about 1.5×10¹⁶ to 2.0×10²⁰ atoms cm⁻³. A gatestructure overlies the first region of the fins; and source/drains areformed on the second regions of the fins.

In another embodiment of the disclosure, a Gilbert-cell mixer isprovided including a plurality of transistors electrically connected toeach other. At least one of the transistors includes one or more finsextending in a first direction over a substrate. The one or more finsinclude a first region along the first direction and second regions oneither side of the first region along the first direction. The firstregion of the fins includes a dopant in a concentration of about1.5×10¹⁶ to 2.0×10²⁰ atoms cm⁻³. A gate structure overlies the firstregion of the fins and source/drains are formed on the second regions ofthe fins.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A method for manufacturing a semiconductordevice, comprising: forming one or more fins extending in a firstdirection over a substrate, wherein the one or more fins include a firstregion along the first direction and second regions on both sides of thefirst region along the first direction; implanting a dopant in the firstregion of the fins but not in the second regions; forming a gatestructure overlying the first region of the fins; and formingsource/drains on the second regions of the fins.
 2. The method formanufacturing a semiconductor device of claim 1, wherein the dopant isan N-type dopant, selected from the group consisting of P, As, and Sb.3. The method for manufacturing a semiconductor device of claim 1,wherein the dopant is a P-type dopant, selected from the groupconsisting of B, BF₂, Al, and Ga.
 4. The method for manufacturing asemiconductor device of claim 1, wherein a concentration of the dopantin the first region is about 1.5×10¹⁶ to 2.0×10²⁰ atoms cm⁻³.
 5. Themethod for manufacturing a semiconductor device of claim 4, wherein theconcentration of the dopant in the first region is about 1×10¹⁸ atomscm⁻³ to 2×10¹⁸ atoms cm⁻³.
 6. The method for manufacturing asemiconductor device of claim 1, further comprising: forming a resistlayer over the fins; and forming openings in the resist layer to exposethe first region of the fins prior to implanting the dopant.
 7. Themethod for manufacturing a semiconductor device of claim 1, furthercomprising removing the resist layer after implanting the dopant.
 8. Asemiconductor device comprising: one or more fins extending in a firstdirection over a substrate, wherein the one or more fins include a firstregion along the first direction and second regions on either side ofthe first region along the first direction, and the first region of thefins includes a dopant in a concentration of about 1.5×10¹⁶ to 2.0×10²⁰atoms cm⁻³; a gate structure overlies the first region of the fins; andsource/drains are formed on the second regions of the fins.
 9. Thesemiconductor device of claim 8, wherein the dopant is an N-type dopant,selected from the group consisting of P, As, and Sb.
 10. Thesemiconductor device of claim 8, wherein the dopant is a P-type dopant,selected from the group consisting of B, BF₂, Al, and Ga.
 11. Thesemiconductor device of claim 8, wherein the concentration of the dopantin the first region is about 1.7×10¹⁷ to 1.7×10¹⁹ atoms cm⁻³.
 12. Thesemiconductor device of claim 11, wherein the concentration of thedopant in the first region is about 1×10¹⁸ atoms cm⁻³ to 2×10¹⁸ atomscm⁻³.
 13. The semiconductor device of claim 8, wherein N-type dopant iscentered at region in the fin located at about 15 to 20 nm from a top ofthe fin and 3 to 7 nm in a fin thickness direction from a sidewallextending along the first direction of the fin.
 14. The semiconductordevice of claim 8, further comprising a plurality of fins; and anisolation insulating layer formed between adjacent fins.
 15. Thesemiconductor device of claim 8, having a gate length between source anddrain regions of about 7 nm to about 16 nm.
 16. The semiconductor deviceof claim 8, wherein the gate structure comprises a high-k gatedielectric layer and a metal gate electrode.
 17. The semiconductordevice of claim 8, wherein the source/drain regions are raisedsource/drain regions.
 18. A Gilbert-cell mixer comprising: a pluralityof transistors electrically connected to each other, wherein at leastone of the transistors comprises: one or more fins extending in a firstdirection over a substrate, wherein the one or more fins include a firstregion along the first direction and second regions on either side ofthe first region along the first direction, and the first region of thefins includes a dopant in a concentration of about 1.5×10¹⁶ to 2.0×10²⁰atoms cm⁻³; a gate structure overlies the first region of the fins; andsource/drains are formed on the second regions of the fins.
 19. TheGilbert-cell mixer of claim 18, wherein the dopant is centered at regionin the fin located at about 15 to 20 nm from a top of the fin and 3 to 7nm in a fin thickness direction from a sidewall extending along thefirst direction of the fin.
 20. The Gilbert-cell mixer of claim 18,wherein the dopant is an N-type dopant selected from the groupconsisting of P, As, and Sb.